The invention relates generally to photo imaging on nonplanar substrates, and more particularly, to an imaging system using a corrective diffractive optical element with an ellipsoidal mirror for focusing a two dimensional image onto a three dimensional substrate.
Conventional integrated circuits, or "chips," are formed from two dimensional or flat surface semiconductor wafers. The semiconductor wafer is first manufactured in a semiconductor material manufacturing facility and is then provided to a fabrication facility. At the latter facility, several layers are processed onto the semiconductor wafer surface, including various circuit design images, to create a very large scale integrated ("VLSI") design. Although the processed chip includes several layers fabricated thereon, the chip remains relatively flat.
A fabrication facility is relatively expensive due to the enormous effort and expense required to create flat silicon wafers and chips. Moreover, the wafers produced by the above processes typically have many defects which are to the above cutting, grinding and cleaning processes as well as due to the impurities, including oxygen, associated with containers used in forming the crystals. These defects become more and more detrimental as the integrated circuits formed on these wafers become smaller.
Another major problem associated with modern fabrication facilities for flat chips is that they require extensive and expensive equipment. For example, dust-free clean rooms and temperature-controlled manufacturing and storage areas are necessary to prevent the wafers and chips from defecting and warping. Also, these types of fabrication facilities suffer from a relatively inefficient throughput as well as an inefficient use of the silicon. For example, facilities using in-batch manufacturing, where the wafers are processed by lots, must maintain huge inventories to efficiently utilize all the equipment of the facility. Also, because the wafers are round, and the completed chips are rectangular, the peripheral portion of each wafer cannot be used.
Still another problem associated with modern fabrication facilities is that they do not produce chips that are ready to use. Instead, there are many additional steps that must be completed, including cutting and separating the chip from the wafer; assembling the chip to a lead frame which includes wire bonding, plastic or ceramic molding and cutting and forming the leads, positioning the assembled chip onto a printed circuit board; and mounting the assembled chip to the printed circuit board. The cutting and assembly steps introduce many errors and defects due to the precise requirements of such operations. Additionally, the positioning and mounting steps are naturally two-dimensional in character, and therefore do not support curved or three-dimensional areas.
U.S. patent Ser. No. 08/858,004 entitled SPHERICAL SURFACE SEMICONDUCTOR INTEGRATED CIRCUIT, herein incorporated by reference as if produced in its entirety, describes a three dimensional, sphere-shaped substrate for receiving various circuits. Of the many process disclosed in the above-referenced application, several are related to imaging a circuit design onto the three dimensional substrate. Often, the circuit design to be imaged may be two dimensional in nature.
One solution for imaging a two-dimensional circuit design to a three-dimensional object, such as a sphere, is to use an elliptical mirror system. However, there are numerous problems associated with the elliptical mirror system for reflecting the image onto the sphere's surface. Referring to FIG. 1, a collimated beam 10 is shown reflecting off of an elliptical mirror 12. The elliptical mirror 12 has two focus points and an image emerging from one focus point is reflected by the elliptical mirror and refocus at the second focus point. As the beam 10 passes through the first focus point of the elliptical mirror 12 at various angles, the beam 10 is reflected toward the second focus point, and towards a spherical semiconductor device 14 located near the second focus point.
In actuality, the beam 12 focuses at a point 16, which is one of an infinite number of points on a best focus surface 18 that emerges between the surface of the elliptical mirror 12 and the device 14. The best focus surface 18 is not spherical. Instead it is aspheric in shape and not compatible with projecting and focusing images on the surface of a spherical semiconductor. As a result, the image on at least some portions of the spherical surface is out of focus.
Therefore, what is needed is an apparatus and a method for reshaping the best focus surface to more closely match the surface geometry of a sphere.